RV-7 flap pos ind

Just found out I can use a spare input on my G3X to display flap position. I noticed some guys using the Ray Allen POS-12. Probably a stupid question but, why not the POS-5 or POS-7? Also, is there anyone who offers a complete kit with all materials and instructions?

Size matters

The only difference in the units is in the range of travel. If you can use a smaller radius of action off of the attach point so you stay inside the max range, any will work.